From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0D39F30C620; Fri, 9 Jan 2026 14:46:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767969995; cv=none; b=AV5pDFA054tuwlQ05VDbVskxYvcTKgPk6Yf/FcpnZcjB613kT8DZGiUpjQvDCg82v3yqUPTnTkAZvcjHKBLks5POB2/wLKRmjcx1d9j/qqrY/43tRrLzcR7KdZHZvOw/dEHTFpvycGpKdgWI6gteaTx01jFOH+jwnHQbd6wIKeg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767969995; c=relaxed/simple; bh=TiX3+Mf2/1XrF5Wi9iq9L5ZAotC8Ji5SdKgsf6S+mLw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BxkAIjj91otOBv8/Gia8byAIVbTqhwBGF9cDnGi+JI/RBhfVf5J7ukBzPuFJtOkgiGLAFk6J+K5m4L1nZy+6gbDOUwbieQjNlTK4PfkZ64VLKuA50loQTv9p+xNwdNed764y+E0I6cPmSo7mwKpz0gU5U+CbDtER6VpbcBF6BUY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uZUjYGj2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="uZUjYGj2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE468C4CEF1; Fri, 9 Jan 2026 14:46:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767969994; bh=TiX3+Mf2/1XrF5Wi9iq9L5ZAotC8Ji5SdKgsf6S+mLw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=uZUjYGj2vzAU/895Kp1TsSc1LFPAvhNfYFyiQDT/1sHdc86Fb7CYXvrSKCDHqJ9l9 OSWqCHO0/cYPa3ylDhqf6y820RTSZtL93ba0/jGN1oVlEHjGaHVVykQ3MCU+Z6yj5W Stp2vxGoONL9lIG5qlLIvwPqw495ZXWRGOcbNNcduB2d9QF46/J+RZy3jhW8UW+Yoe 5lypxi/zl4Ku7tZnxaxkw12IeQII5MIXEcGtCs7SxEBmWncna6ityUGGr3As4XirRc zrtFEF64kiJCzQIJjj/FtQi84qhO0pj2g1lozr3UvVSKZgWbxb5zl5K461ANhI+fVX rz+yJMFWSC3+A== Message-ID: <3cc27720-8f53-4b6f-9202-42b3b73928b8@kernel.org> Date: Fri, 9 Jan 2026 15:46:26 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 2/2] mm/khugepaged: retry with sync writeback for MADV_COLLAPSE To: Shivank Garg , Andrew Morton , Lorenzo Stoakes Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Zach O'Keefe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Branden Moore References: <20251215084615.5283-3-shivankg@amd.com> <20251215084615.5283-7-shivankg@amd.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: <20251215084615.5283-7-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/15/25 09:46, Shivank Garg wrote: > When MADV_COLLAPSE is called on file-backed mappings (e.g., executable > text sections), the pages may still be dirty from recent writes. > collapse_file() will trigger async writeback and fail with > SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN). > > MADV_COLLAPSE is a synchronous operation where userspace expects > immediate results. If the collapse fails due to dirty pages, perform > synchronous writeback on the specific range and retry once. > > This avoids spurious failures for freshly written executables while > avoiding unnecessary synchronous I/O for mappings that are already clean. > > Reported-by: Branden Moore > Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com > Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE") > Suggested-by: David Hildenbrand > Tested-by: Lance Yang > Signed-off-by: Shivank Garg > --- > mm/khugepaged.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 219dfa2e523c..6c8c35d3e0c9 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -22,6 +22,7 @@ > #include > #include > #include > +#include > > #include > #include "internal.h" > @@ -2787,9 +2788,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > hend = end & HPAGE_PMD_MASK; > > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > + bool retried = false; > int result = SCAN_FAIL; > > if (!mmap_locked) { > +retry: Jumping into an if block is nasty :) > cond_resched(); > mmap_read_lock(mm); > mmap_locked = true; > @@ -2819,6 +2822,43 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > if (!mmap_locked) > *lock_dropped = true; > > + /* > + * If the file-backed VMA has dirty pages, the scan triggers > + * async writeback and returns SCAN_PAGE_DIRTY_OR_WRITEBACK. > + * Since MADV_COLLAPSE is sync, we force sync writeback and > + * retry once. > + */ > + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !retried) { > + /* > + * File scan drops the lock. We must re-acquire it to > + * safely inspect the VMA and hold the file reference. > + */ > + if (!mmap_locked) { > + cond_resched(); > + mmap_read_lock(mm); > + mmap_locked = true; > + result = hugepage_vma_revalidate(mm, addr, false, &vma, cc); > + if (result != SCAN_SUCCEED) > + goto handle_result; > + } > + > + if (!vma_is_anonymous(vma) && vma->vm_file && > + mapping_can_writeback(vma->vm_file->f_mapping)) { > + struct file *file = get_file(vma->vm_file); > + pgoff_t pgoff = linear_page_index(vma, addr); > + loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; > + loff_t lend = lstart + HPAGE_PMD_SIZE - 1; > + > + mmap_read_unlock(mm); > + mmap_locked = false; > + *lock_dropped = true; > + filemap_write_and_wait_range(file->f_mapping, lstart, lend); > + fput(file); > + retried = true; > + goto retry; > + } > + } > + This looks a bit complicated. Can't we move that handing up, where we have most of that information already? Or am I missing something important? diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 97d1b2824386f..c7271877c5220 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include "internal.h" @@ -2786,7 +2787,9 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { int result = SCAN_FAIL; + bool triggered_wb = false; +retry: if (!mmap_locked) { cond_resched(); mmap_read_lock(mm); @@ -2809,6 +2812,16 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, mmap_locked = false; result = hpage_collapse_scan_file(mm, addr, file, pgoff, cc); + + if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && + mapping_can_writeback(file->f_mapping)) { + loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; + loff_t lend = lstart + HPAGE_PMD_SIZE - 1; + + filemap_write_and_wait_range(file->f_mapping, lstart, lend); + triggered_wb = true; + goto retry; + } fput(file); } else { result = hpage_collapse_scan_pmd(mm, vma, addr, -- Cheers David